Telephone circuits for individual telephone and computer data transmission lines are normally routed through a cable head wherein each circuit is connected to a receptacle that mates with a protective plug. The plug has a coil and carbon-gap feature that serves as a fuse upon appearance of excess current in its circuit from lightning or other sources of stray current. In effect each plug acts as a normally closed relay, opening upon exposure to excess current and providing a path to ground when open. The cable head is in the form of a rectangular insulating block having an array of a large number of receptacles, typically one hundred, arranged in spaced-apart relationship on the block. Banks of cable heads stacked one one another are normally located in telephone central offices so as to provide centralized access to the protective plugs for all telephone lines.
While disabled plugs are readily available for replacement in this arrangement, obtaining electrical access to wires of individual circuits for purposes of troubleshooting and testing has proven difficult. In order to utilize test equipment that may include computerized systems for analyzing and determining circuit conditions, wires of the individual circuit must be located and electrically connected to wires of the test equipment. Presently used procedures require that wires leading to cable head sockets for a specific circuit must be identified from hundreds of other wires feeding outward from the cable head assembly into a common conduit. Tip and ring wires for the circuit would then be stripped of insulation and spliced to wires leading to test equipment. The circuit would then be broken between the central office and outside lines. This provides for interactive testing of the disconnected circuits. In addition to being time-consuming, this procedure entails a risk of damaging circuit wires that are stripped as well as other wires and insulation. A need thus exists for more convenient and effective access to circuits in the cable head.